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Astrophysics > Earth and Planetary Astrophysics

Title:Exoplanet Atmosphere Measurements from Direct Imaging

Abstract: In the last decade, about a dozen giant exoplanets have been directly imaged
in the IR as companions to young stars. With photometry and spectroscopy of
these planets in hand from new extreme coronagraphic instruments such as SPHERE
at VLT and GPI at Gemini, we are beginning to characterize and classify the
atmospheres of these objects. Initially, it was assumed that young planets
would be similar to field brown dwarfs, more massive objects that nonetheless
share similar effective temperatures and compositions. Surprisingly, young
planets appear considerably redder than field brown dwarfs, likely a result of
their low surface gravities and indicating much different atmospheric
structures. Preliminarily, young free-floating planets appear to be as or more
variable than field brown dwarfs, due to rotational modulation of inhomogeneous
surface features. Eventually, such inhomogeneity will allow the top of
atmosphere structure of these objects to be mapped via Doppler imaging on
extremely large telescopes. Direct imaging spectroscopy of giant exoplanets now
is a prelude for the study of habitable zone planets. Eventual direct imaging
spectroscopy of a large sample of habitable zone planets with future telescopes
such as LUVOIR will be necessary to identify multiple biosignatures and
establish habitability for Earth-mass exoplanets in the habitable zones of
nearby stars.

Comments:

29 pages, 8 figures, authors' updated version of invited review chapter accepted for publication in the Handbook of Exoplanets